Exhaust stack



FIG. 1 is a perspective view of an exhaust stack showing my new design;

FIG. 2 is a bottom plan view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left end elevation view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a right end elevation view thereof;

FIG. 7 is a front elevation view thereof; and

FIG. 8 is a cross-sectional view of FIG. 3 along section lines 8--8. 

The ornamental design for an exhaust stack, as shown. 